Should Biology Matter?

I just finished reading an article advocating that the word parent be redefined to include any one who has an active role in the child's life. According to the article, the suppliers of the eggs and sperms that created the child should have no more rights to the child than a person who develops a social relationship with the child. In the context of my own writing, I thought about how maternity should be determined in surrogacy arrangements. Should the woman who is biologically linked to the child always be presumed to be the child's legal mother? Some courts have said yes.